NO. 4 WIND TUNNEL EXPERIMENTS IN AERODYNAMICS 47 



abaft the center of buoyancy. The ship is therefore stable. At lo 

 degrees angle of yaw, the resultant force passes nearly through the 

 center of buoyancy, and if the ship should get in this position the pilot 

 would have to use slightly more than i6| degrees rudder angle to 

 bring her back. 



The conclusion from these tests is that with the size rudder and 

 fin fitted, 7.79 and 3.47 square inches, the ship can be held on her 

 course by the use of not more than 16^ degrees of rudder. 



The importance of an adequate vertical rudder is apparent, since 

 the weights give no restoring moment for yawing as they do for 

 pitching. 



It appears impossible in practice to give sufficient vertical fin area 

 to hold the ship on her course without use of the helm. 



VH. PITCHING AND YAWING MOMENTS ON xMODEL OF 

 CURTISS AEROPLANE CHASSIS AND FUSELAGE, 

 COMPLETE WITH TAIL AND RUDDER, BUT WITH- 

 OUT WINGS, STRUTS, OR PROPELLER 



By J. C. HUNSAKER and D. W. DOUGLAS 



A wood model of the Curtiss tractor body, complete with all 

 appendages except wings, was constructed to a scale i inch to the 

 foot and 24.5 inches actual length. The model was held in its ordi- 

 nary position in the wind tunnel by a vertical spindle attached to the 

 balance. The angle of yaw was varied, and observations were made 

 to determine the components of force directed down stream and 

 across the stream, as well as the twisting moment about a vertical 

 axis passing through the supporting spindle. The axis of the model 

 was kept in a horizontal plane during this test. 



The model was then removed from the spindle shown in figure 13, 

 side elevation. A new spindle was set into the side of the model as 

 shown in figure 13, plan. The model was again placed in the wind 

 tunnel but now lay on its side. Rotation about the new spindle axis 

 made it possible to set the model at various angles of pitch, the angle 

 of yaw being held constant. Measurements were made as above of 

 down stream and cross stream components of force, and moment 

 about the axis of the spindle. 



